1. Field of the Invention
The disclosure relates to a technique for inspecting deformation of a substrate holding member which is configured to hold a substrate to transport the same, and which is mounted on a transport base of a substrate transport apparatus and is movable in a forward-and-backward direction relative to the transport base.
2. Description of Related Art
In manufacturing of semiconductor devices or liquid crystal displays, a substrate processing system having plural processing modules is used. Substrates (e.g., semiconductor wafers) are transferred between the processing modules by using a substrate transport apparatus installed in the substrate processing apparatus, and the substrates are subjected to predetermined processes in the processing modules. The substrate transport apparatus has a transport base and forks (wafer holding members) each for holding the periphery of a wafer which are mounted to the transport base and are movable in a forward-and-backward direction relative to the transport base. The transport base is rotatable about a vertical axis and is vertically movable.
In the substrate processing system, a specific transfer position is set at which a wafer is transferred from the substrate transport apparatus to a processing module and vice versa. The fork of the substrate transport apparatus is moved to the transfer position, and the wafer is transferred between the fork and the processing module. If the transfer position is set inappropriately, the fork may collide with any structural member of the processing module. In a case where the fork receives a wafer from a processing module holding the wafer in an inappropriate position, or in a case where a wafer slips on the fork due to a liquid adhering to the wafer, the wafer may be held on the fork at an inappropriate position. In such cases, the wafer may collide with any structural member of the processing module. If the aforementioned collision occurs, the fork may become deformed such that the fork bends upward or downward, or the open ends of the fork are narrowed or widened. Continuous operation of the deformed fork may result in a secondary accident, such as falling of the wafer from the fork, and further collision of the fork with any structural member, which may break the wafer, the fork or the substrate transport apparatus.
In order to avoid such a secondary accident, if the fork collides with any structural member to trigger an alarm, the operator enters the interior space of the substrate processing system, and conducts visual inspection for the deformation of the fork according to the inspection manual, and conducts maintenance (repair) if the fork is deformed. It is difficult to determine the condition of the fork precisely, because the interior space of the substrate processing system is narrow and darkish. In addition, due to a large numbers of items to be inspected, the operator bears a heavy burden. The preciseness of the visual inspection depends on the operator's skill, and thus quantitative judgment of the fork deformation is difficult.
US2008/0232937A1 (JP2008-235841A) discloses a substrate transport apparatus having a transport base and horizontally-extending holding arms, and having an inspection device for inspecting whether or not the posture of the holding arms with respect to the horizontal plane is normal. The inspection device has an optical sensor forming a horizontal light path. The transport base moves vertically so that the holding arms, moves across the light path, and based on the detection signal of the optical sensor indicating “light reception”/“no light reception” and the height of the transport base, whether or not the posture of each holding arms is normal is judged.
The inspection method taught by US2008/0232937A1 is advantageous for judging whether or not the posture of vertically-arrayed holding arms is normal can be judged at one time, but can hardly judge whether or not local deformation occurs in the holding arms.